Same build system and everything, it just requires some finagling and copying of the PKGBUILDs.
Indeed, we really want people attached to or passionate about the projects we provide packages for to jump on board. There's loads of interesting work to do, so please consider rolling your sleeves up.
vim configs are often different per-platform anyway. I have an if mac/else block in my gvimrc, since gfn, for example, requires "Font:hSize" on OS X and another type of font selector on Linux-based systems. Things like that are not really new.